The present invention relates to a new and improved construction of a self-adjusting regulation system which automatically adjusts itself to an optimum circuit configuration in accordance with the characteristics of its regulation circuit.
The theory of regulation systems is well known, yet the designations used hereinafter in this disclosure will be defined in order to clarify the significance thereof:
The feedback magnitude is the magnitude which should be maintained at a reference value; it is the output magnitude of the load and an input magnitude of the regulator. A disturbance magnitude is that magnitude which has some influence upon the feedback magnitude, with the exception of the adjustment magnitude. The adjustment magnitude is that magnitude by means of which there is intentionally acted upon the feedback magnitude in order to eliminate the effect of the disturbance magnitude; it is the output magnitude of the regulator and an input magnitude of the load. The command magnitude is that magnitude which determines the reference value of the feedback magnitude; it is an input magnitude of the regulator. The regulation path is that portion of the regulation system where there is produced the feedback magnitude; the adjustment magnitude and possible disturbance magnitude are algebraically added and processed within the load. The regulator is that part of the regulation system where there is produced the adjustment magnitude; the command magnitude, the feedback magnitude and possible disturbance magnitudes are added and processed within the regulator. The feedback circuit consists of the load, the regulator and the connections which enable the proper delivery of the enumerated magnitude; in the event for instance owing to different physical characteristics the feedback magnitude cannot be directly utilized as the input magnitude of the regulator then it is converted by a sensor or feeler located in the regulation circuit into an input magnitude suitable for the regulator; in the event that for analogous reasons the adjustment magnitude cannot be directly utilized as the input magnitude of the load, then it is converted into an input magnitude suitable for the load by an adjustment element located in the regulation circuit.
The characteristics of the components of the regulation circuit are to be considered as known and generally possess imperfections which occur either for technical reasons or are brought into existence owing to the operating conditions of the regulation system. The latter for instance is the case if for operational reasons the feedback magnitude or the adjustment magnitude are subjected to conditions which limit their value or their changes, so that the normally linear characteristics of the regulation circuit become non-linear.
For instance, in a regulation system for the alignment of a target tracking theodolite in azimuth or elevation, the open regulation circuit normally possesses a linear transmission function. If, however, the current in a drive motor of the theodolite reaches a value which should not be exceeded, although the proper target tracking function would require a greater current, then a device which limits the current becomes effective in the regulation circuit and which permits the transmission function of the open regulation circuit to become non-linear.
In such type regulation system, the open regulation circuit of which possesses a linear or non-linear transmission function, depending upon the operating conditions, once there have been determined the characteristics of the regulation circuit it is not possible to obtain an optimum circuit configuration throughout the entire useful frequency bandwidth of the regulation system, i.e. to reduce as required the error of the different times derivatives of the feedback magnitudes (for instance position-, velocity-, acceleration- and impact errors) throughout the entire useful frequency range. A fine accommodation of the regulation circuit to the behaviour of the regulation system for achieving the smallest possible regulation errors in the range of the low frequencies leads to instability as soon as the regulation circuit, especially the open regulation circuit, no longer operates in a strictly linear manner. Under these conditions it is necessary, when optimizing the regulation circuit in the range of the low frequencies, to take into account the possibly occurring maximum non-linearity, so that in the normal instance of the linear behaviour there arises a loss in the precision of the regulation which must be accepted in favor of avoiding instability.
A further example of such type regulation system relates to the regulation of the temperature of a body wherein the disturbance magnitude is constituted by the thermal loss and the adjustment magnitude is constituted by an electrical current which delivers thermal energy to the body by the Joule effect. In this system the adjustment magnitude is constituted by an electrical resistor where there is developed the Joule-thermal energy, and which imposes upon the system the condition that the current should not exceed a certain value otherwise the resistor will become damaged or burn-out. A still further example of a similar type regulation system relates to the regulation of the pH-value of a solution wherein the disturbance magnitude is a pH-increase owing to a chemical reaction and the adjustment magnitude is an electrical current which actuates a valve, the opening of which controls the inflow of an acidic solution. In this system the adjustment element is constituted by the valve and a non-linearity arises when there is obtained the maximum inflow of the acidic solution which is governed by the conduit.
For these or similar regulation systems there is to be realized a stable regulation under all operation conditions with maximum precision provided that the optimization of the regulation circuit with regard to the precision of the regulation at the range of the lower frequencies is not limited by the required taking into account of the non-linear behaviour of the regulation circuit.
It is known to optimize the regulation circuit in two separate steps: Initially the characteristics of the regulator are accommodated to the situation of a linear behaviour of the regulation circuit in such a manner that there is realized the best obtainable regulation; thereafter there is provided a correction device which, upon the occurrence of non-linearity in the regulation circuit, modifies certain parameters thereof in such a manner that also in the case of maximum non-linearity there is realized the best obtainable regulation and in particular there does not arise any instability.
For instance, there is disclosed in U.S. Pat. No. 3,510,737 a regulation system for a positioning motor wherein the input magnitude of the regulator is divided into a low frequency portion and a high frequency portion and both such portions are separately processed in the regulator to a respective portion of the adjustment magnitude. Moreover, in the case of a linear behavior of the regulator the adjustment magnitude is formed from the sum of both portions. In the non-linear case the low-frequency portion of the adjustment magnitude is made equal to null and there is only effective the high frequency portion so that there can be reduced the overshooting of the feedback magnitude. With this known solution of the stability problem it is disadvantageous that the adjustment magnitude, when shifting from the linear case to the non-linear case or vice versa, changes in a jump-like or sudden manner, which can bring about undesired loads in the regulation system and, additionally, renders difficult switching of the system from a start-up in the manually-controlled mode of operation or the computer controlled mode of operation to the self-regulating mode of operation. At the moment of closing of the regulation circuit the transmission function of the regulator can assume one of two possible values, depending upon whether previously the open regulation circuit was operated in the linear range or in the non-linear range. Therefore, the command magnitude introduced manually or by the computer with the open regulation circuit is not unambiguously equivalent in its action to a single predeterminable feedback magnitude which is fed back to the regulator with closed regulation circuit.
In the German patent publication No. 2,226,882 there is proposed a method for the stabilization of a regulation system, the tendency towards instability of which is predicated upon the non-linearity of a saturatable component. Monitoring for non-linearity occurs and there is produced an appropriate control signal which brings about a change of the regulation circuit. This change resides in that upon the occurrence of a non-linearity the gain of the feedback loop is increased in order to realize a transmission function which restores the regulation system again close to the stability limit. In other words, the reduction of the gain of the regulator at the region of the low frequencies brought about by a non-linearity of the regulator is compensated in that the gain of the feedback loop is increased and at the input of the regulator there is reduced the sum of the command magnitude and the feedback magnitude and the regulation system again almost becomes stable because the regulator has again been operated at the limit of the linear range. With this known solution for the stability problem, the adjustment magnitude indeed does not alter in a surge or jump-like manner when the regulation system shifts from the linear operation to the non-linear operation or vice versa, because the adjustment magnitude remains constant upon saturation of the regulator. But also with this solution there is present the drawback that a surgeless switching of the regulation system from a manual- or computer-controlled operation to the self-regulating operation is not insured for at any moment in time, since also in this case at the instant of closing of the regulation circuit the transmission function between the feedback magnitude and the adjustment magnitude can assume one of two possible values, depending upon whether previously the open regulation circuit was operated in the linear range or in the non-linear range.